John Sterling’s memories are vivid, and they are specific. Back in the day, Sterling was the voice of both the Nets and the Islanders on old WMCA radio, sometimes doing as many as 120 games a year. He was living in Manhattan, near the radio stations offices at 57th and Seventh, and making the drive east was every bit as challenging in the mid-’70s as it is now.

And worth the aggravation every blessed time.

“A vibrant, glorious time,” he said yesterday. “For both of those teams.”

Saturday night was for the Islanders, who quickly became the pride of the locals, kids from West Hempstead and Floral Park and East Williston who had a franchise of our very own that waited about 15 minutes to start challenging the Flyers and the Rangers. Sunday afternoon was for the Nets, and the kids from North Bellmore and Bethpage and Oyster Bay really had something to call our own.

“Islanders games were a party,” Sterling remembers. “Full house after full house. Nets games? One time Julius Erving was having a Julius game. There was a sequence where he dunked a ball, stole it, made an unbelievable pass, blocked a shot, and then Kevin Loughery, the coach, called a timeout because he figured that was the only way he could get an audible round of applause.”

It was a good day to be talking about those years, or a terrible day, depending on how you look at it. The Nets returned to Nassau Coliseum for the night, hosting the Knicks exactly 29 miles east of Barclays Center, where the same two teams will open the season next Thursday. The game, which the Knicks won 97-95, was a sellout. That was the good.

Six hours earlier, the Islanders had announced they will be joining the Nets in Brooklyn soon. That was the bad. Look, this isn’t the Dodgers and Giants bailing for California. For one thing, convenience aside, 30 miles isn’t 3,000. For another, the Islanders haven’t exactly been a Saturday-night hot ticket for decades.

Still, if you were a Long Island kid in those heady days of the ’70s, if you were growing up at the same time Nassau and Suffolk counties were reaching for a slice of the big time, and the big leagues, it was hard not to be torn apart with bursts of bittersweet as you walked through the Coliseum’s creaky corridors yesterday.

Joe Namath spent a summer living two blocks from my house in the summer of ’74. Two years ago the Jets abandoned Hofstra and Hempstead Turnpike for their shiny and soulless new digs in Jersey.

Scooter Barry, Rick’s son, went to grade school for a year with me, and I played with Billy Melchionni, Bill’s boy, in high school. The Nets went Thataway to Piscataway after one Long Island year in the NBA, in ’77.

And the Islanders … well, they gave us four parades up the Turnpike. They gave us a folk hero named Chico Resch, who almost drove us to glory in the spring of ’75 then became the most popular backup in the history of backups. For four years they allowed an island of miserable Jets and Mets fans to feel what it was like to root for the Giants and the Yankees.

Of course, that was a long, long time ago.

“At its best,” Sterling said yesterday, “it was a utilitarian building. And it hasn’t been at its best for quite a few years.”

The Islanders couldn’t stay here, and in time it will be better for everyone that they chose Brooklyn instead of Quebec City or Kansas City. The Nets took a quick look at yesteryear yesterday before hightailing it for their gleaming new home, and will never look back. Soon enough, the building itself will be a mall, or an apartment complex, and nobody will remember the Van Halen concerts, the Billy Joel concerts, or Squeeze, or Zeppelin, or Elton John.

Besides, memories aren’t always the most reliable resource. Sterling cites Game 7 of the ’76 ABA semifinals, a vicious series in which Nets forward Rich “House” Jones became a folk hero, a sellout crowd of 15,934 lugging signs — “THIS IS HOUSE’S HOME!” “YOU CAN’T BLOW OUR HOUSE DOWN!” — and making a ruckus as Jones went for 25 and 11 and the Nets stomped the Spurs.

“But there were many more games where there were 5,000 people in there,” he said. I looked it up. He’s right. Funny: Yesterday, it was almost impossible to remember it that way.